Major goal of this investigation is to study the role of vitamin A on the cell cycle kinetics of the hamster respiratory tract resulting from various exposure to 10 ppm of nitrogen dioxide gas exposure. The effect of vitamin A on the injury and repair mechanism due to NO2 gas has been measured by employing various techniques such as electron and light autoradiography, scintillator counting, both scanning and transmission electron microscpy and immunological techniques. BIBLIOGRAPHIC REFERENCES: Netlesheim, P., Snyder, C.M., Williams, M.L., Cone, M.V. and Kim, J.C.S.: Effect of Vitamin A on Lung Tumor Induction in Rats. Proc. Am. Assoc. Cancer Res., 16: 54, 1975. Kim, J.C.S., Jourden, M.G., and Carlisle, E.S.: The effect of vitamin A on the intermittent nitrogen dioxide gas exposure in hamsters. Proc Electron Soc Amer (Claitors Publishing Co, New Orleans, LA; F. B. Bailey, Ed), 1976 (in press).